Magnetic materials



Patented Oct. 24, 1944 MAGNETIC MATERIALS Joy F. Dillinger, Riverside,and Arthur N. Ogden, Chicago, Ill., assignors to Western ElectricCompany, Incorporated, New York, N. Y., a corporation of New York NoDrawing. Application October 21, 1942, Serial No. 462,844

4 Claims.

This invention relates to magnetic materials and to a method ofpreparing the same, and more particularly tomagnetic materials to beused as stabilizers and a method of preparing the same.

Magnetic bodies comprising compressed, finely divided magnetic materialin the form of dust or assembled thin laminations of magnetic materialare extensively used as cores for loading coils, filtering coils,transformers and similar transmission apparatus in telephone circuits.The transmission characteristics of such apparatus are subject tovariations due to changes in the permeability of the cores with changesin temperature under service conditions, These variations areparticularly objectionable in the case of high quality precisioncircuits.

In order to prevent these variations, a magnetic material, which has asuitable permeability temperature coefiicient as compared with that ofthe core material, may be added to the primary core material tocompensate for variations due to temperature. Such a material isgenerally referred to as a stabilizer.

As described in U. S. Patent 2,158,132, issued to V. E. Legg, May 16,1939, a magnetic core having a substantially constant permeability overa desired temperature range may be prepared by forming the core from amixture of a magnetic material such as Permalloy, which may compriseapproximately 82% nickel, 16% iron and 2% molybdenum and which has apositive permeability temperature coeflicient over the range oftemperature from 55 F. to 125 F., and a proper amount of dust of asecond magnetic material having a negative permeability coefiicient overthat temperature range. A magnetic material having such a negativepermeability coefiicient may comprise approximately 80% nickel, 12% to13 molybdenum and the rest iron. Such a material, when used with thefirst described magnetic material, serves as a stabilizer of thepermeability of the magnetic core.

Molybdenum tends to oxidize during melting, and the oxide so formedtends to volatilize. This results in a loss of some of the molybdenum,and since a variation in the amount of molybdenum present in thestabilizer of even 1% will result in a change in the Curie point of thestabilizer of approximately 100 F., it will be apparent that the exactpermeability temperature coefiicient of the stabilizer material willdepend largely on the molybdenum present in the final stabilizer dust.Furthermore, an ingot formed from a melt containing a known amount ormolybdenum and the other aforementioned materials will have areas ofdiiiering permeability and differing Curie points. This appears to bedue to a segregation of molybdenum particles during cooling and appearsto be unavoidable even in the most thoroughly mixed melts.

An object of the present invention is to provide an effective andefflcient method of obtaining stabilizer materials having predeterminedmagnetic properties.

In accordance with one embodiment of this invention, magnetic materialmay be powdered and the powder passed through a magnetic separatingmachine a number of times at increasing tem-, peratures to obtainmaterials having increasingly higher Curie points.

In accordance with another embodiment of this invention, a powderedmagnetic material may be passed a number of times through a magneticseparator under increasing field strengths at a constant temperature toobtain materials having progressively lower Curie points.

Other objects and advantages of this invention will be apparent from thefollowing detailed description.

This invention will be described in connection with the production ofmagnetic materials having Curie points between 55 F. and 125 F. It willbe understood, however, that the method of this invention is applicableto the production of magnetic materials having Curie points within anydesired feasible range.

In the practice of this invention, an ingot of magnetic material isprepared by melting together approximately nickel, 12% to 13% molybdenumand the rest iron. These materials maybe melted together in any suitablefurnace to produce an alloy. Melting is carried out in a non-reducingatmosphere, in general, and some compensation must be made for the lossof molybdenum during melting by the addition of extra molybdenum inadvance. In practice this loss has been found to amount to not more than.25%. However, because of the considerable effect on the Curie point ofthe stabilizer material of even a slight change in the amount ofmolybdenum present, it is desirable to control the amount of molybdenumin the final alloy within very close limits so far as possible.

The ingot is then hot rolled and the fragments reduced to powder. Inorder to keep contamination due to wear at a minimum, an impact typemachine may be used for pulverization and the powder reduced toapproximately '400 mesh fineness.

In accordance with one embodiment of this invention, the powder soobtained may then be passed through a magnetic separator at atemperature of approximately 50 F. Material, the Curie point of whichhas been reached will be separated into one group by the separator,while material having a higher Curie point will be separated intoanother group. The latter group of material is then passed through theseparator at a temperature of, for example, 55 F. to obtain magneticmaterials having Curie points at approximately 55 F. On successivepasses, the temperature may be raised and the process repeated with thematerial left until materials having a sumcient range of Curie pointsare obtained. The field strength of the magnetic separator must, ofcourse, be maintained constant and the precise field strength. to beused will depend upon the area of the magnetic field and the amount ofmaterial being passed thereunder at a given time. By removing in advancematerial having a Curie point lower than that which it is desired toobtain, in addition materials having lower permeabilities andnon-magnetic materials, are substantially removed and, in subsequentpasses, the material which will be segregated will be substantiallypurely magnetic, differing only as to Curie points. It will be apparentthat the first separating pass could be made at a high temperature, andthereafter successive passes made at relatively lower temperatureswithout departing from the spirit or scope of this embodiment of thepresent invention.

In accordance with another embodiment of this invention, where it is notfeasible to control the temperature of the magnetic material as it ispassed through the magnetic separator within the close limits required,magnetic materials having varying Curie points maybe satisfactorilysegregated by maintaining a constant temperature and varying the fieldstrength of the magnetic separator.

The magnetic material is prepared and powdered in the same way asdescribed hereinbefore. The powder so obtained is then heated to atemperature of approximately 180 F., and the heated powder spread out ina very thin layer on the separator belt. The temperature of the materialshould be so controlled so that the powder on the belt is approximately140 F. to 170 F. as it falls on the belt. This may be dete: mined byholding a thermometer in the stream of powder as it falls on the belt.The portion of the powder which is discharged on the nonmagnetic side ofthe separator is used for further processing and that portion of powderdischarged on the magnetic side is discarded as unsuitable for use as astabilizing powder in the range of 55 F. to 125 F. This roughpreliminary separation of the powder is particularly necessary wherematerials are to be separated by varying th field strength since even inthe most closely controlled melts, material having varyingpermeabilities at the same temperature oothe eparation between themagnetic poles of the separator. For the first pass, the field strengthshould be so adjusted that between 10% and 2.0% of the material isdischarged on the magnetic side of the separator. In successive passes,the field strength should be increased so that approximately 20% of thematerial is discharged on the magnetic side ''of the separator in eachpass. If the current has been increased to the maximum possible and alarge percentage of the material still remains in the non-magneticportion, the field strength should be further increased by moving thepoles closer together.

As a magnetic material approaches its Curie point, its permeabilitydecreases sharply; thus. greater field strength is required in a magnetto attract a material near its Curie point than a material not near itsCurie point, assuming the materials are equal in permeability. Thus. inthe first pass after the rough separation, the material having thehighest Curie point will be discharged on the magnetic side of theseparator and, in successive passes, material having Curie pointsprogressively lower will be discharged on the magnetic side of theseparator.

It has been found in practice that the accuracy of separation by eitherembodiment of this invention is substantially the same, the advantage ofthe former method of separation over the latter described being that thelatter will not distinguish between one material which has a lowpermeability due to its proximity to the Curie point and another whichis far removed from its Curie point, but inherently of low permeability,whereas the former will so distinguish. However, in the latter case, bycarefully controlling the composition of the melt and by making therough preliminary separation described, this difliculty is largelyobviated.

The magnetic core is then formed by using a small amount of a stabilizerpowder comprising particles having a plurality of Curie points over therange of 55 F. to 125 F. Stabilizer materials having more than one Curiepoint are used our, and since materials having Curie points so as tostabilize the temperature permeability coeiflcient over the whole rangedesired rather than at only one temperature. In practice, beforecombining portions of the separated groups of magnetic material, it maybe desirable to test each group to determine accurately the magneticcharacteristics thereof and thereby to determine precisely whatproportions of each group to employ to obtain a mixture having thedesired properties.

Using permalloy dust, as hereinbefore described, to form a magnetic coreinsulated, for example, as described in the patent to A. F. Bandur, 2105,070, issued January 11, 1938, the permeability of a core so formedmay be stabilized over a range of temperature from 55 F. to F. by theaddition of 2% to 1% stabilizer powder of the type herein described inmost cases. The minimum amount of stabilizing powder which willaccomplish the desired stabilization is used because of the highhysteresis loss of the stabilizer material.

While but two embodiments of this invention have been shown anddescribed, it will be under stood that many changes and modificationsmay be made therein without departing from the spirit or scope of thepresent invention.

What is claimed is:

1. A method of forming a stabilizer material for magnetic cores, saidmaterial comprising particles having a variety of Curie points, saidmethod comprising powdering a magnetic material composed ofapproximately 80% nickel, 12% to 13% molybdenum, and the rest iron,passing the powdered material through a magnetic separator at atemperature lower than the temperature of the lowest desired Curie pointand then passing the remaining material through the separator atsuccessively higher temperatures to obtain particles having a'variety ofCurie points,

2. A method of preparing a stabilizer material for magnetic cores, saidmaterial comprising particles having a variety of Curie points, saidmethod comprising powdering a magnetic material composed ofapproximately 80% nickel, 12% to 13% molybdenum and the rest iron, andsuc cessively passing the powdered material through a magneticseparating device at increasing temperatures, the particles the Curiepoint of which has been reached being discharged on the nonmagnetic sideof the separator.

3. A method of forming a stabilizer material for magnetic cores, saidmagnetic material having a variety of Curie points and composed ofapproximately 80% nickel, 12% to 13% molybdenum and the rest iron,comprising heating the material to between 140 F. to 180 F., passingthis heated material through a magnetic separator to remove all materialhaving a Curie point above that temperature, and then successivelypassing the remaining material through the separator at a lowertemperature and under increasing field strengths to obtain materialshaving varying Curie points.

4. A method of forming a stabilizer composing particles having a varietyof Curie points for magnetic cores, comprising heating a comminutedmixture composed of approximately 80% nickel, 12% to 13% molybdenum andthe rest iron to a temperature above that of the highest Curie pointdesired, passing this heated material through a magnetic separator toremove substantially all material having a Curie point above thattemperature, successively passing the remaining material through theseparator at a lower temperature and under increasing field strengths toobtain materials having varying Curie points, and then recombiningportions of the variously separated materials to obtain a stabilizermaterial having the desired characteristics.

JOY F. DIILINGER. ARTHUR N. OGDEN.

